There is general agreement that a rotavirus vaccine for infants and young children is needed in both developed and developing countries because: (1) rotaviruses are the single most important etiologic agents of severe diarrhea in infants and young children world-wide, causing 35-50% of these illnesses; (2) rotaviruses are an important cause of morbidity in developed countries and a major cause of morbidity and mortality in developing countries in children less than 5 years of age; (3) there is no therapeutic drug for the specific treatment of rotavirus diarrhea. (Although, oral rehydration salt solutions are a well-recognized therapeutic measure for diarrheal illnesses of varying etiology including rotaviruses, the availability, use and implementation of this regimen remains problematic in many parts of the world); and (4) hygienic measures appear to have little effect on the transmissibility of rotavirus because about 90% of infants and young children develop a rotavirus infection by the end of the third year of life in both developed and developing countries. We have developed a modified Jennerian approach to vaccination and have formulated a quadrivalent vaccine containing: (i) rhesus rotavirus (RRV) (VP7:3) and (ii) three human rotavirus--RRV reassortants, each possessing ten RRV genes and a single human rotavirus gene that encodes VP7 (the major protective antigen) serotype 1, 2, or 4 specificity. Two major field trials reported in 1995 or 1996, and a third which was recently described, demonstrated at least 80% protection against severe rotavirus diarrhea in infants and young children, raising expectations that a licensed rotavirus vaccine may be on the horizon. In addition, generally encouraging signals regarding efficacy of the rotavirus vaccine in developing or underdeveloped areas indicate that the vaccine can provide protection in selected areas where it is needed most.